Programmable integrated circuits have applications in all manner of devices. Many of the commodity electronic devices that we take for granted, such as cellular telephones, PDA's, music players and radios, have at least one programmable component among the circuitry on their printed circuit board (PCB). In the manufacturing of millions of these electronic devices yearly, each of the programmable integrated circuits are typically programmed and tested with the rest of the components on the board. With high volume manufacturing flow, it is desirable that the interaction with a single programmable integrated circuit be straight forward and fast. It is also desirable that the device be programmed and verified in as short a time as possible, with minimal interaction involving the in-circuit tester (ICT).
Early generations of PCB in-circuit testers used a functional testing methodology where test signals were applied at various circuit inputs and output signals were monitored by the ICT. Such functional testing suffers from at least two limitations. First, it can be difficult to formulate thorough and effective test programs suitable for gathering information concerning a variety of circuits designated for test because of the unique nature of individual circuits. Second, fault isolation to a particular element on a PCB or other circuit assembly having many circuit elements may require an accurate operational understanding of the assembled circuit.
It is often difficult to analyze sequential devices, e.g., devices that require a series of signal changes at the input before any change is detected on the output. The complicated nature of the relationships between test signals applied at circuit inputs and the resulting signals at the outputs of the individual sequential device makes it extremely difficult to determine the signals that may need to be applied at the circuit assembly inputs to “initiate” each sequential device in the circuit assembly. As a result of the limitations of functional testing, many circuit assembly testers utilize a technique known as in-circuit testing in which individual circuit components (both sequential and non-sequential) are tested via in-circuit application of test signals at the inputs of each component and concurrent observation of resulting output signals at the various outputs of each component.
For simple circuits, testing is often accomplished by applying appropriate voltages to circuit nodes to test for short or open circuits. Circuit nodes are any equipotential circuit element, such as, but not limited to, connecting wires, printed circuit board traces, edge connectors, and connector pins. Functional testing methods as described above may also be performed where the tester and/or test equipment has sufficient knowledge of circuit operation. As circuit assemblies become more complex, circuit testers have to adapt in order to accurately and thoroughly test these complex assemblies. With the added complexity and density due to miniaturization, it has become more important, and more difficult, to thoroughly test circuit assemblies.
Generally, typical automated circuit assembly tests include a host computer running a test program (i.e., a software application) that operates a test interface that communicates various steady-state voltages and test signals between test equipment and the device under test (DUT). The test interfaces may access the various test ports as well as other circuit nodes on the DUT. The test equipment may include numerous resources, such as voltage drivers, receivers, relays, and test pins arranged to engage appropriate locations of the DUT. The drivers and receivers are alternately connected and may be jointly connected in some embodiments (as for bidirectional data busses) in a systematic and clocked sequence to various nodes of the DUT. The drivers and receivers may be connected via relays and test pins that contact various circuit assembly nodes, giving the test equipment control of the embedded circuitry.
When the embedded circuitry includes programmable devices, the test program can become very complicated and spend an inordinate amount of time managing the programming and test process for a single device. If the in-circuit tester is engaged in programming a single embedded integrated circuit, all of the other nodes of the DUT may be held at a neutral state. Once the programmable device has been programmed, the entire DUT may be put into a state that will allow positive testing of the programmable device as well as its surrounding circuits. As a result the in-circuit tester programs can be significantly longer and require more resources within the in-circuit tester to execute properly. The overwhelming nature of this problem has typically caused manufacturers to program all programmable devices on another station prior to the assembly of the PCB or assemble sockets for later insertion of a programmed device. This option can cause double handling of all PCB's and an extra set of programming stations in the manufacturing flow.